Rotational atherectomy system with stationary cutting elements

ABSTRACT

An elongate tubular body extends between a rotatable cutter and a control. The cutter is connected to the control with a rotatable element. A vacuum is applied through an annular passage defined between the tubular body and the rotatable element. The cutter has at least one radial projection which cooperates with at least one stationary element on the tubular body to cut material drawn into the tubular body. Material that has been processed by the cutter is aspirated through the tubular body for disposal.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. patent application Ser. No.09/592,218, filed Jun. 12, 2000, now U.S. Pat. No. 6,451,036, which is acontinuation of U.S. patent application Ser. No. 09/398,241, filed Sep.17, 1999, now U.S. Pat. No. 6,666,874 which is a continuation-in-part ofU.S. patent application Ser. No. 09/260,199, filed Mar. 1, 1999, nowU.S. Pat. No. 6,206,898, which is a continuation-in-part of U.S. patentapplication Ser. No. 09/058,513, filed Apr. 10, 1998, now U.S. Pat. No.6,001,112.

BACKGROUND OF THE INVENTION

The present invention generally relates to medical devices and, moreparticularly, to atherectomy catheter devices.

A variety of techniques and instruments have been developed to removeobstructive material in arteries or other body passageways or to repairthe arteries or body passageways. A frequent objective of suchtechniques and instruments is the removal of atherosclerotic plaques ina patient's arteries. The buildup of fatty deposits (atheromas) in theintimal layer (under the endothelium of a patient's blood vessels)characterizes atherosclerosis. Over time, what is initially deposited asrelatively soft, cholesterol-rich atheromatous material often hardensinto a calcified atherosclerotic plaque. The atheromas may be referredto as stenotic lesions or stenoses while the blocking material may bereferred to as stenotic material. If left untreated, such stenoses canso sufficiently reduce perfusion that angina, hypertension, myocardialinfarction, strokes and the like may result.

Several kinds of atherectomy devices have been developed for attemptingto remove some or all of such stenotic material. In one type of device,such as that shown in U.S. Pat. No. 5,092,873 (Simpson), a cylindricalhousing, carried at the distal end of a catheter, has a portion of itsside-wall cut out to form a window into which the atherosclerotic plaquecan protrude when the device is positioned next to the plaque. Anatherectomy blade, disposed within the housing, is then advanced thelength of the housing to lance the portion of the atherosclerotic plaquethat extends into the housing cavity. While such devices provide fordirectional control in selection of tissue to be excised, the length ofthe portion excised at each pass of the atherectomy blade is necessarilylimited to the length of the cavity in the device. The length andrelative rigidity of the housing limits the maneuverability andtherefore also limits the utility of the device in narrow and tortuousarteries such as coronary arteries. Such devices are also generallylimited to lateral cutting relative to the longitudinal axis of thedevice.

Another approach, which solves some of the problems relating to removalof atherosclerotic plaque in narrow and tortuous passageways, involvesthe use of an abrading device carried at the distal end of a flexibledrive shaft. Examples of such devices are illustrated in U.S. Pat. No.4,990,134 (Auth) and U.S. Pat. No. 5,314,438 (Shturman). In the Authdevice, abrasive material such as diamond grit (diamond particles ordust) is deposited on a rotating burr carried at the distal end of aflexible drive shaft. In the Shturman device, a thin layer of abrasiveparticles is bonded directly to the wire turns of an enlarged diametersegment of the drive shaft. The abrading device in such systems isrotated at speeds up to 200,000 rpm or more, which, depending on thediameter of the abrading device utilized, can provide surface speeds ofthe abrasive particles in the range of 40 ft/sec. According to Auth, atsurface speeds below 40 ft/sec his abrasive burr will remove hardenedatherosclerotic materials but will not damage normal elastic soft tissueof the vessel wall. See, e.g., U.S. Pat. No. 4,990,134 at col. 3, lines20-23.

However, not all atherosclerotic plaques are hardened, calcifiedatherosclerotic plaques. Moreover, the mechanical properties of softplaques are very often quite close to the mechanical properties of thesoft tissue of the vessel wall. Thus, one cannot always rely entirely onthe differential cutting properties of such abrasives to removeatherosclerotic material from an arterial wall, particularly where oneis attempting to remove all or almost all of the atheroscleroticmaterial.

Moreover, a majority of atherosclerotic lesions are asymmetrical (i.e.,the atherosclerotic plaque is thicker on one side of the artery than onthe other). As will be understood, the stenotic material will beentirely removed on the thinner side of an eccentric lesion before itwill be removed on the thicker side of the lesion. Accordingly, duringremoval of the remaining thicker portion of the atherosclerotic plaque,the abrasive burr of the Auth device or the abrasive-coated enlargeddiameter segment of the drive shaft of the Shturman device willnecessarily engage healthy tissue on the side that has been cleared.Indeed, lateral pressure by such healthy tissue against the abradingdevice is inherently required to keep the abrading device in contactwith the remaining stenotic tissue on the opposite wall of thepassageway. For stenotic lesions that are entirely on one side of anartery (a relatively frequent condition), the healthy tissue across fromthe stenotic lesion will be exposed to and in contact with the abradingdevice for substantially the entire procedure. Moreover, pressure fromthat healthy tissue against the abrading device will be, in fact, theonly pressure urging the abrading device against the atheroscleroticplaque. Under these conditions, a certain amount of damage to thehealthy tissue is almost unavoidable, even though undesirable, and thereis a clear risk of perforation or proliferative healing response. Insome cases, the “healthy tissue” across from a stenotic lesion may besomewhat hardened by the interaction (i.e., it has diminishedelasticity); under such circumstances, the differential cuttingphenomenon described by Auth will also be diminished, resulting in arisk that this “healthy” tissue may also be removed, potentially causingperforation.

Thus, notwithstanding the foregoing and other efforts to design arotational atherectomy device, there remains a need for such a devicethat can advance through soft atheromas while providing minimal risk ofdislodging emboli, and risk of injury to the surrounding vessel wall.

SUMMARY OF THE INVENTION

There is provided in accordance with one aspect of the presentinvention, a rotational medical device. The device comprises an elongateflexible tubular body, having a proximal end and a distal end. Arotatable element extends through the body. A rotatable tip at thedistal end of the body is connected to the rotatable element. A controlis provided on the proximal end of the body. At least one radiallyinwardly extending stationary cutting member is provided on the tubularbody, and at least one radially outwardly extending flange on therotatable tip is provided for cooperating with the stationary cuttingmember to cut material drawn into the tubular body.

In one embodiment, the device comprises two radially outwardly extendingflanges on the tip. The device may also comprise two stationary cuttingmember on the tubular body. The device may further comprise an annularrecess in the tubular body, for rotatably receiving the radiallyoutwardly extending flange. The distal end of the rotatable tip may beeither approximately aligned axially with the distal end of the tubularbody, extend beyond the distal end of the tubular body, or be recessedwithin the tubular body.

In accordance with another aspect of the present invention, there isprovided a method of removing material from a vessel. The methodcomprises the steps of providing an elongate flexible tubular body,having a proximal end and a distal end, a rotatable tip at the distalend of the tubular body, and at least on stationary cutting member onthe tubular body which cooperates with at least one flange on therotatable tip. The distal end of the tubular body is advancedtransluminally to the material, and the rotatable tip is rotated.Portions of the material are drawn proximally past the rotatable tip sothat the material is cut by the action of the flange rotating past thestationary member.

Preferably, the drawing step is accomplished by applying vacuum to theproximal end of the tubular body. The advancing step generally comprisesadvancing the tubular body along a guidewire. Preferably, the advancingstep additionally comprises advancing the tubular body through apercutaneous access site.

In one aspect of the invention, the method further comprises the step ofinfusing fluid through a flush port on the proximal end of the tubularbody. The advancing step is accomplished by applying axial distalpressure on the tubular body, and may include the step of reducing theamount of axial distal pressure in response to feedback indicating achange in load on the rotatable tip.

In accordance with a further aspect of the present invention, there isprovided a method of removing material from a patient. The methodcomprises the steps of providing an elongate flexible tubular body,having a proximal end, a distal end, and at least two radially inwardlyextending stationary cutting members near the distal end. A rotatabledistal tip is carried by the distal end of the tubular body, the tiphaving at least two radially outwardly extending flanges, and a controlon the proximal end of the tubular body. The distal tip of the tubularbody is advanced to the material to be removed, and the control ismanipulated to activate a vacuum through the tubular body. Rotation ofthe rotatable tip is commenced to remove material from the patient, andmaterial is sheared between the flanges and the stationary cuttingmembers.

Further features and advantages of the present invention will becomeapparent to those of skill in the art in view of the disclosure herein,when considered together with the attached drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of a device embodying the present invention;

FIG. 2 is a partially sectioned side view of a distal end of the deviceof FIG. 1, showing an embodiment of the cutter assembly;

FIG. 3 is a side view of the cutter of FIG. 2;

FIG. 4 is an end view of the cutter of FIG. 3 taken along the line 4-4;

FIG. 5A is a partially sectioned side view of another embodiment of thecutter and housing;

FIG. 5B is a cross-sectional view of the cutter and housing of FIG. 5Ataken along the lines 5B-5B;

FIG. 6 is a partially sectioned side view of yet another cutter andhousing;

FIG. 7 is a partially sectioned side view of a further cutter andhousing;

FIG. 8A is a top perspective view of a serrated cutter configured inaccordance with certain features, aspects and advantages of the presentinvention;

FIG. 8B is a side view of the serrated cutter of FIG. 8A;

FIG. 8C is a top view of the serrated cutter of FIG. 8A;

FIG. 9 is a sectioned side view of a control having features, aspectsand advantages in accordance with the present invention;

FIG. 10A is a schematic illustration of a pinch-valve switch in aposition which interrupts an applied vacuum and interrupts power flow toa drive motor;

FIG. 10B is a schematic illustration of a pinch-valve switch in aposition that applies the vacuum and interrupts power flow to the drivemotor;

FIG. 10C is a schematic illustration of a pinch-valve switch in aposition which applies the vacuum and allows power to flow to the drivemotor;

FIG. 11 is a schematic illustration of a representative motor controlcircuit in accordance with the present invention;

FIG. 12 is an enlarged partially sectioned side view of a cutter,housing and catheter assembly configured in accordance with certainaspects and advantages of the present invention;

FIG. 13 is a schematic view of a treatment process performed accordingto a first mode of off-set operation; and

FIG. 14 is a schematic view of a treatment process performed accordingto a second mode of off-set operation.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

With reference initially to FIG. 1, a surgical instrument, indicatedgenerally by reference numeral 10 having features, aspects andadvantages in accordance with the present invention is depicted therein.In general, the illustrative surgical instrument comprises an elongateflexible tubular body 12 having a proximal end 14 and a distal end 16. Acontrol 18 is preferably provided at or near the proximal end 14 of thetubular body 12 for permitting manipulation of the instrument 10. Thecontrol 18 advantageously carries electronic controls and indicators aswell as vacuum controls as will be discussed below.

With reference now to the partially sectioned view of FIG. 2, thetubular body 12 preferably has an elongate central lumen 20. Desirably,the tubular body 12 has a cutter housing 21 for receiving a cutter 22that may rotate therein. The illustrated cutter 22 is coupled to thecontrol 18 for rotation by way of an elongate flexible drive shaft 24,as will be described below. In an over-the-wire embodiment, the driveshaft 24 may also be provided with an axially extending central lumen 26for slidably receiving a guidewire 28 as will be understood by those ofskill in the art. Moreover, in such configurations, the cutter 22 mayalso have a central lumen.

The diameter of the guidewire 28 is preferably in the range of about0.010 inch to about 0.020 inch. The lengths of the guidewire 28 and thetubular body 12 may be varied to correspond to a distance between apercutaneous access site and a lesion being treated. For example, theguidewire 28 and the tubular body 12 should be long enough to allow thecutter 22 of the present surgical instrument 10 to track along theguidewire 28 and reach a target occlusion while also allowing a proximalportion of the guidewire 28 to remain exterior to the patient formanipulation by the clinician (not shown). In an application forremoving coronary artery atheroma by way of a femoral artery access,guidewires having lengths from about 120 cm to about 160 cm may be used,and the length of the tubular body 12 may range between about 50 cm andabout 150 cm, as will be understood by those of skill in art. For otherapplications, such as peripheral vascular procedures includingrecanalization of implanted vascular grafts, the length of the guidewire28 and the tubular body 12 may depend upon the location of the graft orother treatment site relative to the percutaneous or surgical accesssite. Suitable guidewires for coronary artery applications include thosemanufactured by Guidant or Cordis.

With reference now to FIGS. 3 and 4, the illustrated cutter 22 includesa generally cylindrical sleeve shaped body 30 having a central lumen 32(FIG. 4). The cylindrical body 30 of the cutter 22 generally has anexternal diameter of between about 0.035 and 0.092 inch. In oneembodiment, the external diameter is approximately 0.042 inch. The body30 has a wall thickness between about 0.003 inch and about 0.010 inch.In one embodiment, the wall thickness is about 0.009 inch. The length ofone embodiment of the present cutter 22 from proximal end 34 to distalend 36 is approximately 0.096 inch but the length may vary from about0.040 inch to about 0.120 inch or more, depending upon the intended use.In general, tip lengths of no more than about 0.100 inch are preferred;shorter tip lengths permit greater lateral flexibility and enableincreased remote access as will be apparent to those of skill in theart.

With continued reference to FIG. 3, an end cap 38 may be formed on thedistal end 36 of the present cutter tip 22. Specifically, thecylindrical body 30 may be machined to create an integral (i.e., onepiece) end cap 38. The end cap 38 may have a thickness of approximately0.007 inch; however, the end cap thickness may range from about 0.003inch to about 0.020 inch. Additionally, it is contemplated that adiscrete end cap 38 may also be separately machined and attached. Forinstance, the end cap 38 may be formed from a more lubricious materialto reduce frictional contact between the guidewire 28 and the end cap38. Such an end cap may be attached in any suitable manner. The end cap38 preferably has an outside diameter that substantially corresponds tothe outside diameter of the distal end 26 of the present cutter tip 22.The end cap outside diameter may, however, substantially correspond tothe inside diameter of the cylindrical body in some embodiments.

The end cap 38 may also have a centrally located aperture 39. Theaperture 39, if present, preferably has a diameter of between about0.013 inch and about 0.025 inch. In one embodiment, the aperture 39 hasa diameter of approximately 0.022 inch. Desirably, the aperture 39 mayaccommodate a guidewire 28 or allow fluids to flow therethrough. As willbe appreciated, the cutter 22 may have a machined or otherwiseintegrally formed radially inwardly extending annular flange 41 (seeFIG. 6). It is also anticipated that aspects of the present inventionmay also be practiced without employing an end cap or inwardly extendingannular flange 41. In such configurations, the flange 41 may extendfully around the circumference of the cutter 22 or may have portionsremoved such that the annular flange 41 is actually a series of inwardlyprojecting tabs. Additionally, an outside distal edge of the end cap 38or annular flange 41 is desirably broken, chamfered or rounded such thatany sharp edge resulting from manufacturing may be removed, and suchthat the end cap may be rendered substantially atraumatic.

With reference now to FIGS. 2-4, a connector portion 40 is preferablyprovided at or near the proximal end 34 of the illustrated cutter 22 forsecuring the cutter 22 within the cutter housing 21 such that the cuttermay rotate therein. Additionally, the connector portion 40 may be amechanical, self-locking method to secure the rotating cutter 22 withinthe cutter housing 21 and to guard against undesired axial movement ofthe cutter 22 relative to the housing 21. In certain embodiments, axialmovement of the cutter may be accommodated within the housing 21, andeven within the tubular body 12, as will be discussed below in moredetail.

As will be recognized by those of skill in the art, safety straps,redundant glue joints, crimping, and swaging are commonly used to createredundant failure protection for catheter cutter tips. The advantageousstructure of the present connector portion 40 retains the cutter tip 22within the cutter housing 21 and may reduce the need for such multipleredundancies. As will be described, the connector portion 40 may takevarious forms.

In embodiments similar to the one illustrated in FIGS. 2-4, theconnector portion 40 generally comprises two outwardly extending radialsupports, such as a set of wedge-shaped flanges 42. The flanges 42 maybe formed by removing material from an annular circumferential flange atthe proximal end 34 of the cutter 22. The flanges 42 may be formed intothe illustrated wedge-shape, although other shapes may also bedesirable. The flanges 42 may also be bent from a proximal extension ofthe wall of tubular body 30, or adhered or otherwise secured to theproximal end 34 of the cutter 22. Moreover, as will be recognized by oneof ordinary skill in the art, the cutter 22 and flanges 42 may be castor molded using any suitable method dependent upon the material chosen.As will be recognized by those of ordinary skill in the art, the flanges42 may alternatively be connected to tubular body 30 at a point inbetween the proximal end 34 and the distal end 36 of the cutter tip.

Although two opposing flanges 42 are illustrated in FIGS. 2-4, three ormore flanges 42 may be utilized, as will be apparent to those of skillin the art. In general, the flanges 42 should be evenly distributedaround the circumference of the cutter 22 to improve balance duringrotation of the cutter 22. For example, three flanges 42 wouldpreferably extend radially outward from the cylindrical wall of the body30 on approximately 120° centers. Similarly, four outwardly extendingradial flanges 42 would preferably be located on approximately 90°centers.

With reference now to FIGS. 8A-8C, another configuration of theconnector portion 40 is illustrated therein. In the illustratedconfiguration, the outwardly extending radial supports 42 are alsoformed by removing material from an annular circumferential flange atthe proximal end of the cutter 22. The supports 42 are attached to thebalance of the cutter 22 with tangs 43 that are carved from the cutter22 when the supports 42 are formed. In this manner, the tangs 43 do notrequire the slots that form the arms described above. Of course, acombination of the slots and arms and the tangs without slots may alsobe used to attach the flange 42 to the cutter 22. In the illustratedembodiment, the tangs 43 preferably are between about 0.010 inch andabout 0.050 inch in length. More preferably, the tangs 43 are about0.015 inch long. In one embodiment, the tangs are about 0.25 inch long.The tangs also have a width between about 0.010 inch and about 0.050inch. In a presently preferred embodiment, the tangs have a width ofabout 0.020 inch.

The illustrated connector portion 40 has an outside diameter taken aboutthe opposing flanges 42 of approximately 0.071 inch. Generally, theoutside diameter may range from about 0.057 inch to about 0.096 inch ina device intended for coronary artery applications. The thickness of theflanges 42 in the axial direction (i.e., the dimension normal to theincrease in diameter resulting from the flanges) is about 0.010 inch butmay range from about 0.004 inch to about 0.025 inch. In general, anoutside diameter defined about the flanges 42 may be selected tocooperate with the inside diameter of an annular retaining race orgroove 54 in the housing 21, discussed below, to axially retain thecutter 22 while permitting rotation of the cutter 22 relative to thehousing 21. The thickness of the flanges 42 and the axial width of theretaining groove 54 also are generally designed to either allow axialmovement of the cutter 22 within the housing 21 or to limit or eliminatesubstantial axial movement of the cutter 22 within the housing 21, as isdiscussed below.

With continued reference to now FIG. 3, each illustrated flange 42 ispreferably attached to the cutter 22 by a spring arm 43. Each arm 43 isdefined by two longitudinally extending slots 44 which are formed in thecylindrical wall of the body 30 adjacent each flange 42. The slots 44are preferably about 0.005 inch in width; however the width may rangefrom approximately 0.001 inch to approximately 0.025 inch. The slots 44of the present cutter 22 are also generally at least about 0.025 inch inaxial length along the longitudinal axis of the body 30. One skilled inthe art will readily appreciate that the slots 44 of the present cutter22 can be varied in axial length to vary the length of the cantileveredarm 43 that connects the flanges 42 to the cutter 22. The slots 44, andthe arm 43 defined between the slots 44, and the tangs, allow radialinward compression of the flanges 42 and spring arms 43, or tangs, toease assembly of the cutter 22 within the cutter housing 21 as describedbelow.

Desirably, the cutter 22, and especially the portion containing theslots 44, is made of a material having an adequate spring constant aswill be understood by those of skill in the art. In one embodiment, thecutter 22 is made from a medical grade stainless steel alloy. The chosenmaterial preferably has characteristics including the ability to allowthe cantilevered spring arm 43 to deflect radially inwardly an adequatedistance over the length of the arm 43 without exceeding the elasticlimit of the material (i.e., the deflection is an elastic deformation).As is known, elastic deformations allow structures to deflect andsubstantially return to their initial shape or position. For instance,special hardening methods may be used to maintain the elasticity of theselected material in the deflection range necessary for a specificapplication.

With reference now to FIG. 2, the cutter 22 is snap fit into the cutterhousing 21. Advantageously, the arms 43 may be deflected radially inwardsuch that the cutter 22 may be inserted into the cutter housing 21through an aperture or lumen having a smaller ID than the insidediameter of the retaining groove 54 of the cutter housing 21.Preferably, the cutter 22 is inserted from the distal end of the housing21 and slid proximally through the housing 21 until the flanges 42 snapoutward into the race 54. Thus, the cutter 22 will be retained in thishousing even if it separates from its drive element 24. Desirably, thearms 43 substantially return to their original, relaxed positions withinthe retaining groove 54 the cutter housing 21 following installation. Itshould be appreciated that the arms 43 may also be maintained under aslight bending stress (i.e., the inside diameter of the race 54 may besmaller than the outside diameter about the relaxed flanges 42) ifdesired.

With reference now to FIGS. 2-7, an external element for cutting ormanipulating occlusions, such as thrombus, will be described in detail.The element may include a thread 46 that extends along a portion of theexterior surface of the body 30 of the present cutter 22. The thread 46preferably extends distally from a location on the body 30 that isdistal to the connector 40. The thread 46 may be manufactured using anysuitable technique well known to those of skill in the art.

In one embodiment having a cutter housing 21 with an inside diameter ofabout 0.0685 inch, the major diameter of the thread 46 is approximately0.0681 inch. However, the major diameter of the present thread 46 mayrange from about 0.050 inch to about 0.130 inch or otherwise, dependingupon both the inner diameter of the cutter housing and the intendedclinical application. The thread 46 of the foregoing embodiment has apitch of approximately 0.0304 inch and is desirably helical. The pitchmay range from about 0.005 inch to about 0.060 inch, and may be constantor variable along the axial length of the cutter 22. The thickness ofthe present thread 46 in the axial direction is approximately 0.008inch; however, the thickness may range from about 0.003 to about 0.05,and may be constant or variable along the length of the thread 46. Thus,it is anticipated that the cutters 22 may also have a generally spiralhelix thread.

In some of the illustrated embodiments, the thread 46 extendsapproximately two complete revolutions around the cylindrical body 30.The thread 46 may be a continuous radially outwardly extending ridge asillustrated, or may comprise a plurality of radially outstanding bladesor projections preferably arranged in a helical pattern. The thread 46may extend as little as about one-half to one full revolution around thecutter body 30, or may extend as many as 2½ or 3 or more fullrevolutions around the circumference of the body 30, as is discussedmore below. Optimization of the length of the thread 46 may beaccomplished through routine experimentation in view of the desiredclinical objectives, including the desired maneuverability (i.e.,tractability through tortuous anatomy) and the length of the cutter 22,as well as the nature of the cutting and/or aspiration action to beaccomplished or facilitated by the cutter 22. In addition, while thepresent cutter 22 is illustrated and described as having a singlethread, one skilled in the art will appreciate that the cutter 22 mayalso have multiple threads, a discontinuous thread or no threads.

Referring now to FIGS. 6 and 7, the thread 46 illustrated therein is aconstant pitch and varies in cross-section along its length from arelatively low profile at the distal end 36 to a relatively higherprofile at the proximal end 34 of the cutter tip 22. Such a rampedthread 46 improves performance when the catheter encounters more denseobstructive material. In such an embodiment, the major diameter of thedistal lead 47 of the thread 46 is smaller than the major diameter ofthe thread along the more proximal portions of the cutter shaft 30. Itis anticipated that the pitch of the thread 46 may also vary along withthe profile of the thread 46 to alter the clinical effects accomplished.

As discussed directly above, the pitch of the thread 46 may also bevaried along the axial length of the cutter body 30. Varying the pitchallows a modified function at different points along the axial length ofthe cutter 22, such as a greater axial thread spacing at the distal end36 of the cutter 22 to engage material and a relatively closer axialspacing of the threads at the proximal end 34 of the cutter 22 forprocessing the material. In general, the pitch may range from about0.010 inch at the distal end to about 0.080 inch at the proximal end. Inone embodiment, the pitch at the distal end 36 is approximately 0.034,the pitch at the proximal end 34 is approximately 0.054, and the pitchvaries continuously therebetween. The maximum and minimum pitch,together with the rate of change of the pitch between the proximal end34 and the distal end 36 can be optimized through routineexperimentation by those of skill in the art in view of the disclosureherein.

With reference to FIG. 6, the ramped thread diameter results in a distalportion 36 of the cutter 22 that can extend distally beyond the cutterhousing 21 and a proximal portion 34 of the cutter tip 22 that will beretained within the cutter housing 21. This results, in part, from aradially inwardly extending retaining flange 41 which reduces thediameter of the opening 39 at a distal end 52 of the cutter housing 21relative to an internal bore of the housing 21. As shown in FIG. 3, thedistal portion 45 of the thread 46 may have its leading edge broken,chamfered or rounded to remove a sharp corner or edge. By eliminatingthe sharp corner or edge, the risk of accidental damage to the patientis reduced. The distal edge of the cylindrical body 30 and the flanges42 may also be broken, chamfered or otherwise rounded to eliminate orreduce sharp edges.

With reference to FIG. 2, the outside diameter of the thread 46 in thisembodiment has a close sliding fit with the inside diameter, or innerwall, of the cutter housing 21. In this configuration, the atheromatousmaterial will be avulsed by the threads 46, fed further into the housing21 toward the flanges 42 and chopped or minced by the flanges 42. Tofurther enhance the chopping or mincing action of the flanges 42, astationary member (not shown) or a set of stationary members (not shown)may be positioned such that the rotating flanges 42 and the stationarymember or members (not shown) effect a shearing action. The shearingaction breaks up the strands into shorter sections, which are lesslikely to clog the instrument, as described below. Moreover, the flanges42 may be provided with sharply chamfered leading or trailing edges toalter their cutting action, if desired.

It may be desirable in some embodiments to provide an annular spacebetween the outside diameter of the thread 46 and the inside diameter ofthe cutter housing 21. By spacing the thread 46 apart from the insidewall of the central lumen 20, an annular space is provided for materialto pass through the cutter housing 21 without being severed by thethread 46 of the cutter tip 22. This may be utilized in conjunction withvacuum, discussed below, to aspirate material into the atherectomydevice without the necessity of complete cutting by the thread 46 orflanges 42. This may be advantageous if the rate of material removaleffected by aspiration is higher than the rate at which material removalmay occur with the thread 46 engaging such material. In addition, therotational atherectomy device 10 may more readily aspirate certainlesion morphologies, such as those including portions of calcifiedplaque, if the thread 46 is not required to cut all the way through theaspirated material. In general, the desired radial distance between thethread 46 and the inside wall of the cutter housing 21 will be betweenabout 0.0001 inch and about 0.008 inch, to be optimized in view of thedesired performance characteristics of the particular embodiment. In anembodiment intended solely to aspirate soft atheromas, the cuttingfunction of the thread 46, or the thread 46 itself, may be deletedentirely, so that cutting occurs by the flanges or cutting blocks 42and/or stationary members (not shown) in cooperation with the aspirationprovided by a vacuum source.

Interventions for which an atraumatic distal tip is desired, such as,for example but without limitation, saphenous vein graphs, can be wellserved by an atraumatically tipped cutter 22, as illustrated in FIG. 7.The blunt tip cutter 22 preferably has a bulbous or rounded tip 23 thatextends from the distal end of the cutter 22. The tip 23 preferably hasa radially symmetrical configuration such that upon rotation it presentsa smooth, atraumatic surface for tissue contact. Viewed in sideelevation, such as in FIG. 7, the tip 23 may have a generallyhemispherical, oval, elliptical, aspheric or other smooth curve on itsradial surface with either a curved or truncated (i.e., flat) distalsurface. As will be recognized, the shape of the tip 23 may be varied toachieve desirable effects on the catheter crossing profile or on softatheromas, etc. In general, the tip 23 advantageously minimizes thepossibility of traumatic contact between the healthy wall of the vesseland the thread 46 or other cutting element.

The outside diameter of the tip 23 may range from the outside diameterof the cutter body 30 to the outside diameter of the cutter housing 21.Diameters greater than the housing 21 may also be used, but diameterssmaller than the housing 21 facilitate a smaller crossing profile of theinstrument 10. The axial length of the tip 23 may be varied to suit theintended application, but will generally be within the range of fromabout 0.050 inch to about 0.100 inch in a coronary artery application.

The outside surface of tip 23 may be provided with surface texturing ortreatments. As will be recognized by those of skill in the art, thesurface texturing or treatments may be formed by abrasive coating (i.e.,coating the tip with diamond particles), acid etching or any othersuitable method. The texture or treatments may be on the distal surfaceor the lateral surfaces or both such that a two-stage interaction withthe encountered materials may occur. Thus, the tip can be used forgrinding or otherwise remodeling the encountered materials. For example,an abrasive distal surface can be used to cut through calcified plaque,while a smooth radial surface can compress soft material against thevessel wall to facilitate acceptance into the helical thread 46 of thecutter 22. Varying the distance between the distal end 47 of the thread46 and the proximal end of the tip 23, as well as varying its geometry,can allow adjustments to the cutter aggressiveness. For instance, thethread 46 may extend up to the proximal edge of the tip 23 and allowearly engagement of the encountered materials relative to a cutter 22having a length of unthreaded shaft between the proximal edge of the tip23 and the distal end 47 of the thread 46.

The tip 23 can be integrally formed with the cutter tip 22, such as bymachining techniques known in the art. Alternatively, it can beseparately formed and secured thereto, such as by soldering, adhesives,mechanical interference fit, threaded engagement and the like. The tipcan be machined from a suitable metal or molded or otherwise formed froma suitable polymeric material such as polyethylene, nylon, PTFE orothers known to those of ordinary skill in the art.

Moreover, the cutter tip 22 itself may be machined such that the distalfacing end is serrated or discontinuously formed. The discontinuousthread may comprise a number of inclined surfaces forming distallyfacing teeth. In such cutters, the cutter is more aggressive in theforward direction. With reference to FIGS. 8A-8C, such a cutter tip 22may have serrations 57 formed along the distal end 47 of the thread 46.The serrations may also be positioned on an extended nose portion (notshown) of the cutter. The serrations 57 preferably are formed to extendoutward radially from the center axis of the cutter 22. While theillustrated serrations 57 are formed in a straight line, the serrations57 may also be arcuate in shape to form a sickle-shaped cutting surface.The illustrated serrations 57 preferably have a depth of between about0.0005 inch and about 0.0040. More preferably, the serrations 57 areabout 0.0020 deep. The serrations 57 also preferably are formed with asloping face 59 that is at an angle 1 of between about 45° and about 85°with a longitudinal plane that extends through the axis of rotation. Ina presently preferred arrangement, the sloping face extends at an angleof about 60° relative to the same plane. Moreover, the run of thesloping face 59 is preferably between about 0.0020 inch and about 0.0050inch. In the preferred arrangement, the run is about 0.0035 inch inlength. The serrations in the illustrated cutter extend over only aforward facing portion 45 of the distal end 36 of the cutter 22;however, it is anticipated that the cutter 22 may also comprise aserrated thread that extends the entire length of the thread 46.

In many interventions, it is desirable to have the cutter 22 floatingaxially within the housing 21. FIG. 6 illustrates a cutter 22 arrangedto float axially within the housing 21. Preferably, in suchconfigurations, the cutter 22 is provided with an anti-locking threaddesign. For instance, the thread 46 may be configured such that itcannot jam within the housing 21 at either extreme of axial travel. Sucha configuration may involve having a minimum thread major diameter whichis greater than the diameter of the opening in the distal end of thedevice 10 or having a pitch which is less than the thickness of the ringflange 41 formed at the distal tip of the cutter housing 21. Otherconfigurations may also be readily apparent to those of ordinary skillin the art. The axial travel and the thread design desirably cooperateto allow the cutter 22 to self-adjust to digest soft fibrous material.

The housing 21 may conveniently be assembled from two pieces, to entrapthe cutter 22 therein. The two pieces are then laser-welded or otherwisesecured together. In one embodiment, the housing 21 may be splitlongitudinally, the cutter 22 inserted, and the two pieces may then besecured together. In another presently preferred embodiment, the twopieces may split the housing 21 into a distal component and a proximalcomponent (see FIG. 6). The two components may be assembled to trap thecutter 22 therein and may then be laser-welded or otherwise securedtogether. Such assemblies allow for the cutter 22 to be captured withinthe cutter housing 21 as well as allow for certain relatively loosemanufacturing tolerances for the cutter 22 and the cutter housing 21such as will reduce manufacturing costs. Such assemblies also enablebetter fits because the flanges 42 require less travel (i.e., theflanges 42 do not require deflection for insertion into the housing 21).

Desirably the cutter 22 is positively retained in the cutter housing 21for rotation, as discussed directly above. With reference again to FIG.2, the illustrated housing 21 internally may be a stepped cylinderhaving a proximal end 50 and the distal end 52. In some embodimentsfeaturing axial movement of the cutter 22 relative to the cutter housing21 or tubular body 12, an annular bearing surface 48 (see FIG. 6)provides a proximal limit of travel for the flanges 42 on cutter 22.Notably, the annular bearing surface 48 may be formed within the cutterhousing 22 (as illustrated in FIG. 6) or within the tubular body 12 (notshown).

In a specific coronary artery embodiment, the internal diameter of thedistal portion 52 of the cutter housing 21 is approximately 0.0689 inchand may range from about 0.050 inch to about 0.150 inch. The proximalend 50 of the present cutter housing 21 preferably has an internaldiameter of approximately 0.0558 inch. The internal diameter 50 of theproximal end of the present cutter housing 21 may range from about 0.035inch to about 0.130 inch. At its distal end 52, the cutter housing 21may be provided with a radially inwardly extending retaining lip, suchas flange 41 in FIG. 6, sized and configured such that the cutter 22 iscaptured within the cutter housing 21 and such that the cutter 22 cannotscrew itself out of its captured position within the cutter housing 21.

The exterior diameter of the distal end 52 of the cutter housing 21 inone embodiment is approximately 0.0790 inch; however, the distalexterior diameter may range from about 0.039 inch to about 0.150 inchdepending upon cutter design and the intended clinical application. Thedistal portion 52 of the cutter housing 21 in the illustrated embodimentis about 0.117 inch in length but the length may vary from about 0.020inch to about 0.50 inch. In the embodiment illustrated in FIG. 2, theoutside diameter of the proximal portion 50 of the cutter housing 21 maybe less than the diameter of the distal portion 52 to produce an annularshoulder 51 to limit concentric proximal advance of the proximal sectionwithin the tubular body 12. The proximal section of the housing 50extends axially for approximately 0.09 inch but its length may vary aswill be understood by those of skill in the art.

In general, the cutter housing 21 may be integrally formed or separatelyformed and secured to the distal end 16 of the tubular body 12 inaccordance with any of a variety of techniques which will be known tothose of skill in the art. The concentric overlapping joint illustratedin FIG. 2 can be utilized with any of a variety of secondary retentiontechniques, such as soldering, the use of adhesives, solvent bonding,crimping, swaging or thermal bonding. Alternatively, or in conjunctionwith any of the foregoing, an outer tubular sleeve (not shown) may beheat shrunk over the joint between the cutter housing 21 and the tubularbody 12. While not shown, it is presently preferred to slide theproximal end 50 of the cutter housing 21 over the distal end 16 of thetubular body 12 and apply a fillet of adhesive about the proximalextremity of the cutter housing 21 to hold the two components together.In such a configuration, the proximal portion 50 of the cutter housing21 desirably does not block a portion of the annual recess definedbetween the central lumen 20 and the outer surface of the drive element24. It is anticipated that this style of connection can be utilized withany of the cutter housing features described herein and that the cutterhousing 21 may be provided with an internal stop to limit axialdisplacement of the cutter housing 21 relative to the distal end 16 ofthe tubular body 12.

With reference again to FIG. 2, at the proximal interior end of thedistal component 52 of the housing 21 is the shallow outwardly extendingannular retaining race or groove 54 introduced above. The retaining race54 in one embodiment is approximately 0.0015 inch deep relative to theinner diameter of the distal section 52 and may range in depth fromabout 0.0005 inch to about 0.020 inch. The retaining race 54 in theillustrated embodiment is about 0.0135 inch in axial width; however, asone skilled in the art will readily appreciate, the race width may bevaried and still accomplish its retention function as is discussedfurther below. Moreover, the race 54 may be located proximally, orextend proximally, of the cutter housing 21 such that the cutter 22 maybe retracted within the tubular body 12.

The retaining race 54 cooperates with the flanges 42 of the presentcutter 22 to retain the cutter 22 within the cutter housing 21 asdescribed in detail above. The flanges 42 provide a bearing surface forthe cutter 22 to facilitate rotational movement of the cutter 22relative to the housing 21. In addition, where the axial dimensions ofthe flanges 42 and the race 54 are approximately the same, the cutter 22may be substantially restrained from axial movement within the cutterhousing 21. As will be appreciated, the race 54 may be larger in axialwidth relative to the thickness of the flanges 42 to allow axialmovement of the cutter 22 within the cutter housing 21 or even into thetubular body 12 as discussed above.

With continued reference to FIG. 2, the distal extremity of theillustrated cutter 22 may be approximately aligned with the distalextremity of the cutter housing 21. As such, the length of the cutterhousing 21 distal of the retaining groove 54 substantially correspondsto the length of the portion of the of the cutter 22 which extendsdistally of the distal surfaces of flanges 42. By creating asubstantially flush positioning at the distal end 52 of the cutterhousing 21 and the cutter 22, the possibility of accidental damage tothe intima by the cutter 22 is reduced. One skilled in the art willreadily recognize, however, that the distal end 36 of the cutter 22 mayalternatively extend beyond, or be recessed within, the distal end 52 ofthe cutter housing 21 (i.e., the embodiment of FIG. 7). Additionally,the cutter 22 may be arranged for selective extension and retractionrelative to the cutter housing 21, the benefits of which are describedbelow.

Another cutter 60 and associated cutter housing 70 are illustrated inFIGS. 5A and 5B. Although the cutter 60 embodies many of the samefeatures as the cutter 22 described above, like elements will generallybe called out by new reference numerals for ease of discussion. Itshould be recognized, however, that any of the features, aspects oradvantages of the cutter 22 described above and the cutter 60 describedbelow may be easily interchanged by one of ordinary skill in the art.

The cutter 60 is preferably symmetrical about the rotational axis havinga body 61 with an annular retention structure, such as a retaining race62, located near the body's proximal end 64. The retaining race 62, orconnector portion, in the illustrated embodiment is about 0.007 inchdeep, and about 0.008 inch wide, although both dimensions can be variedas may be desired and still achieve the desired retention function, aswill be readily recognized by one with skill in the art. Proximal to theretaining race 62, the outside diameter of the body 61 is rounded ortapers from about 0.04 inch to about 0.036 inch. Preferably, all edgesare broken, chamfered or otherwise rounded to ensure burr free and dullcorners and to facilitate assembly. The cutter 60 may also have a thread66 similar to that described above.

The cutter 60 is preferably snap fit into the cutter housing 70 byinserting the cutter 60 into the distal end 74 of the cutter housing 70.The cutter housing 70 is preferably similar to that described above withthe exception that the retaining race 54 of the first housing isreplaced by a set of inwardly extending radial retaining members 72.With reference to FIG. 5B, the present cutter housing 70 has threeretaining members 72, preferably circumferentially symmetricallydistributed (i.e., on about 120∞ centers). One skilled in the art willrecognize that the number, size and shape of the retaining members canvary; at least two will generally be used to achieve opposition, andembodiments having 3, 4, 5 or more may be readily utilized. It ispossible, however, to utilize a single retaining member in someapplications such that the single retaining member operates as astationary cutter member either with or without a set of cutter blocks(42 in the embodiments described above).

As with the arms 43 above, the retaining members 72 are sized andconfigured to allow deflection within the elastic range such that theretaining members 72 may be deflected and inserted into the race 62 asdiscussed below. Again, this snap fit configuration advantageouslyenables the cutter 60 to be retained in the cutter housing 70 even ifthe cutter 60 separates from the driving element (not illustrated).

As introduced directly above, the retaining members 72 may serve theadded function of stationary cutting members. As such the retainingmembers 72 may be sized accordingly. The illustrated retaining members72 are about 0.007 inch thick in the axial direction; however, oneskilled in the art will appreciate that the thickness can range fromabout 0.003 inch to about 0.030 inch or otherwise depending uponmaterial choice and the desired degree of axial restraint. The retainingmembers 72 extend about 0.007 inch inward from the interior wall of thecylindrical cutter housing 70. The retaining member 72 length can vary,however, depending upon the desired dimensions of the cutter housing 70and the cutter 60. As shown in FIG. 5B, the side edges 73 of theretaining members 72 may be provided with a radius such that the radialinterior and exterior ends are wider than the central portion.Additionally, while shown with a concave radius, the stationaryretaining members 72 may alternatively be provided with a convex radius(not shown) to form a smoothly transitioning profile.

As one skilled in the art will appreciate, the retaining members 72 areprovided to engage within the retaining race 62 of the cutter 60. Theretaining members 72 and the race 62 may be sized and configured suchthat the cutter 60 is either substantially restrained from axialmovement relative to the cutter housing 70 or some axial travel isallowed between the two components. The retaining members 72 may alsoprovide a bearing surface for the rotational movement of the cutter 60relative to the cutter housing 70. For instance, the race 62 of thecutter 60 desirably rides on the ends of the retaining members 72 suchthat the retaining members 72 provide bearing surfaces at their innermost edges and allow the cutter 60 to be rotated relative to the housing70. Similar to the assembly described above, the distal end 65 of thecutter 60 may be approximately flush with the distal end 74 of thecutter housing 70. Alternatively, the distal end 65 of the cutter 60 mayextend distally from or may be slightly recessed within the distal end74 of the cutter housing 70 by as much or more than is shown in FIG. 5A.Moreover, in specific applications, the cutter 60 may be selectivelyadvanced or retracted relative to the cutter housing 70, enablingadvantages that are described below.

With reference again to FIG. 2, the distal end of a flexible drive shaft24 may be firmly secured within an axial bore 32 of the cutter 22. Thecutter 22 may be secured to the flexible drive shaft 24 by any of avariety of ways such as crimping, swaging, soldering, interference fitstructures, and/or threaded engagement as will be apparent to those ofskill in the art. Alternatively, the flexible drive shaft 24 couldextend axially through the cutter 22 and be secured at the distal end 36of the cutter 22.

In any of the embodiments described herein, the cutter 22 and the cutterhousing 21 may be designed so that the cutter 22 may be positionedwithin the cutter housing 21 in a manner that allows axial movement ofthe cutter 22 relative to the cutter housing 21. Controllable axialmovement of the cutter 22 may be accomplished in a variety of ways, toachieve various desired clinical objectives. For example, in either ofthe embodiments illustrated in FIGS. 2 and 5 a, a minor amount of axialmovement can be achieved by increasing the axial dimension of theannular recesses 54, 62 with respect to the axial dimension of theflanges 42, or retaining members 72. The annular proximal stop 48 (FIG.2) can be effectively moved proximally along the tubular body 12 to aposition, for example, within the range of from about 5 centimeters fromthe distal end 52 to at least about 10 or 20 centimeters from the distalend 52. This permits increased lateral flexibility in the distal 10 cmor 20 cm or greater section of the tubular body 12. Alternatively, theproximal stop 48 can be eliminated entirely such that the entire insidediameter of the tubular body 12 is able to accommodate the flanges 42 ortheir structural equivalent, or the outside diameter of the thread 46,depending upon the embodiment. Limited axial movement can also beaccomplished in the manner illustrated in FIGS. 6 and 7, as will beappreciated by those of skill in the art.

In general, relatively minor degrees of axial movement, such as on theorder of about one or two millimeters or less may be desirable to helpreduce the incidence of clogging and also reduce trauma, such as by thedistal cutting tip pressing against a vessel wall. Minor axialmovability can also help compensate for differential elongation orcompression between the tubular body 12 and the drive shaft 24.

A greater degree of axial movability may be desirable in embodiments inwhich the cutter 22 may be controllably extended partially beyond thehousing 21 such as to improve engagement with hard obstructive material.Retraction of the cutter 22 within the cutter housing 21 may bedesirable during insertion of the device 10, to minimize trauma to thevascular intima during positioning of the device 10. The cutter 22 maythereafter be advanced distally on the order of 1 to 3 or 5 millimetersbeyond the distal end 52 of the housing 21, such as to engageobstructive material to be drawn into the cutter housing 21.

More significant proximal retraction of the cutter 22 within the housing21, such as on the order of 5 to 20 centimeters from the distal end 52,may be advantageous during positioning of the atherectomy catheter. Asis understood in the art, one of the limitations on positioning of atransluminal medical device within tortuous vascular anatomy,particularly such as that which might be encountered in the heart andintracranial space, is the lateral flexibility of the distal portion ofthe device. Even if the outside diameter or crossing profile of thedevice is small enough to reach the stenotic region, the device stillmust have sufficient pushability and sufficient lateral flexibility tonavigate the tortuous anatomy.

In the context of rotational atherectomy catheters, the rotatable driveshaft 24, as well as the cutter 22, can significantly increase therigidity of the catheter. In accordance with the present invention, thedrive shaft 24 and the cutter 22 may be proximally withdrawn within thetubular housing 12 to provide a relatively highly flexible distalcatheter section that is capable of tracking a guidewire 28 throughtortuous vascular anatomy. Once the outer tubular housing 12 of theatherectomy catheter has been advanced to the treatment site, the cutter22 and the drive shaft 24 may be distally advanced through the tubularbody 12 and into position at the distal end 16. In this manner, therotational atherectomy catheter can be positioned at anatomicallocations that are not reachable if the drive shaft 28 and housing 21 atthe distal end 16 of the tubular body 12 are advanced as a single unit.

In general, the cutter 22 is preferably proximally retractable from thedistal end 52 of the cutter housing 21 by a distance sufficient topermit the outer tubular body 12 and cutter housing 21 to be positionedat the desired treatment site. In the context of coronary arterydisease, the distance between the distal end 52 of the cutter housing 21and the retracted cutter 22 is generally be within the range of fromabout 5 cm to about 30 cm and preferably at least about 10 cm. Proximalretraction of the cutter 22 over distances on that order will normallybe sufficient for most coronary artery applications.

The flexible drive shaft 24 is preferably a hollow, laminated flexible“torque tube” such as may be fabricated from an inner thin-wallpolymeric tubing, an intermediate layer of braided or woven wire, and anouter polymeric layer. In one embodiment, the torque tube comprises apolyimide tube having a wall thickness of about 0.004 inch, with a layerof braided 0.0015 inch stainless steel wire embedded therein. Thelaminated construction advantageously produces a tube with a very hightorsional stiffness and sufficient tensile strength, but which isgenerally laterally flexible. However, depending upon the desired torquetransmission, diameter and flexibility, any of a variety of othermaterials and constructions may also be used. In general, the driveshaft 24 should have sufficient torsional rigidity to drive the cutter22 through reasonably foreseeable blockages. It is also recognized thatin some applications, the drive shaft 24 may be a wire or other solidconstruction such that no inner lumen 26 extends therethrough.

The outside diameter of one embodiment of the present hollow flexibledrive shaft 24 is approximately 0.032 inch, but may range between about0.020 inch and about 0.034 inch or more. One skilled in the art willappreciate that the diameter of the flexible drive shaft 24 may belimited by a minimum torsional strength and a guidewire diameter, if aguidewire 28 is present, at the low end, and maximum permissiblecatheter outside diameter at the high end.

The selection of a hollow drive shaft 24 allows the device 10 to beadvanced over a conventional spring-tipped guidewire 28, and preferablystill leaves room for saline solution, drugs or contrast media to flowthrough the lumen 26 of the drive shaft 24 and out of the distal opening39 on the cutter 22. The internal diameter of the present hollowflexible drive shaft 24 is thus partially dependent upon the diameter ofthe guidewire 28 over which the flexible drive shaft 24 must track. Forexample, the internal diameter of the guidewire lumen 26 in oneembodiment of the present hollow flexible drive shaft 24, intended foruse with a 0.018 inch diameter guidewire, is approximately 0.024 inch.Because the flexible drive shaft 24 preferably extends between thecontrol 18 and the cutter 22, the length of the present hollow flexibledrive shaft 24 should be sufficient to allow the cutter assembly toreach the target location while also allowing adequate length outside ofthe patient for the clinician to manipulate the instrument 10.

With reference again to FIG. 2, the lumen 20 of the assembled device 10is thus an annular space defined between the inside wall of the flexibletubular body 12 and the outside of the flexible drive shaft 24. Thislumen 20 may be used to aspirate fluid and material from the cutter.Preferably, sufficient clearance is maintained between the tubular body12 and the rotating drive shaft 24 to minimize the likelihood of bindingor clogging by material aspirated from the treatment site.

In general, the cross-sectional area of the lumen 20 is preferablymaximized as a percentage of the outside diameter of the tubular body12. This permits an optimization of lumen cross-sectional area whichmaintains a minimal outside diameter for tubular body 12, while at thesame time permitting an acceptable flow rate of material through theaspiration lumen 20, with minimal likelihood of clogging or bindingwhich would interrupt the procedure. Cross-sectional area of theaspiration lumen 20 thus may be optimized if the drive tube 24 isconstructed to have relatively high torque transmission per unit wallthickness such as in the constructions described above. In oneembodiment of the invention, intended for coronary artery applications,the outside diameter of tubular body 12 is about 0.080 inch, the wallthickness of tubular body 12 is about 0.008 inch, and the outsidediameter of the drive shaft 24 is about 0.031 inch. Such a constructionproduces a cross-sectional area of the available aspiration portion ofcentral lumen 20 of about 0.00245 square inch. This is approximately 50%of the total cross-sectional area of the tubular body 12. Preferably,the cross-sectional area of the lumen 20 is at least about 25%, morepreferably at least about 40%, and optimally at least about 60% of thetotal cross-sectional area of the tubular body 12.

The tubular body 12 may comprise any of a variety of constructions, suchas a multi-layer torque tube. Alternatively, any of a variety ofconventional catheter shaft materials such as stainless steel, or singlelayer polymeric extrusions of polyethylenes, polyethylene terephthalate,nylon and others well known in the art can be used. In one embodiment,for example, the tubular body 12 is a PEBAX extrusion having an outsidediameter of approximately 0.090 inch. However, the outer diameter canvary between about 0.056 inch for coronary vascular applications andabout 0.150 inch for peripheral vascular applications. Also, because thetubular body 12 must resist collapse under reasonably anticipated vacuumforces, the foregoing tubular body 12 desirably has a wall thickness ofat least about 0.005 inch. The wall thickness can, however, be varieddepending upon materials and design.

The distal end of the tubular body 12 may be affixed to the proximal end50 of the cutter housing 21 as shown in FIG. 2 and described above. Theproximal end of the tubular body 12 may be affixed to the control 18 asdescribed below.

With reference to FIG. 9, the point at which the flexible drive shaft 24is connected to the control 18 is a likely point of damaging bendingforces. As such, a reinforcing tube 80 is desirably provided to reducethe likelihood of a failure at that location due to bending forces. Thereinforcing tube 80 may extend from the control unit 18 along a proximalportion of the tubular body 12. The reinforcing tube 80 preferablyextends distally over the tubular body 12 at least about 3 cm and morepreferably about 6 cm, and desirably comprises silicone or otherconventional biocompatible polymeric material. The illustratedreinforcing tube 80 provides support to avoid over bending and kinkingat the proximal end of the drive shaft 24. With continued reference toFIG. 9, the reinforcing tube 80 may be fastened to the control 18 suchas by interference fit over a snap tip assembly 82 through which theflexible drive shaft 24 and tubular body 12 enter the control 18. Thus,the reinforcing tube 80 advantageously envelops a proximal portion ofthe tubular body 12.

Respectively, the flexible drive shaft 24 and the tubular body 12operatively connect the cutter 22 and the cutter housing 21 to thecontrol 18 of the illustrated embodiment. With continued reference toFIG. 9, the tubular body 12 and the drive shaft 24 enter the control 18through the snap tip assembly 82. The snap tip assembly 82 may beprovided with a connector, such as a hub 84, having a central lumen incommunication with a vacuum manifold 86. The tubular body 12 may beconnected to the hub 84. Specifically, the hub 84 may snap onto and seala vacuum manifold 86 to the hub 84 and, consequently, to the tubularbody 12. The hub material, therefore, desirably provides long-termmemory for snap-fit tabs that secure this part to the rest of theassembly. The presently preferred hub 84 is injection molded using awhite acetyl such as Delrin. The hub 84 may be rotatable, and may enablethe operator to rotate the tubular body 12 relative to the control 18such that the operator, or clinician, may steer the tubular body 12without having to move the control 18 along with the tubular body 12.Friction to limit this rotation may be provided by a bushing 87 that iscompressed against the hub 84 in the illustrated embodiment.

The tubular body 12 may be reinforced internally where it passes throughthe hub 84, such as by a thin-wall stainless steel tube (not shown) thatextends through and is bonded to the hub 84. In general, a goodrotational coupling is desired between the tubular body 12 and the hub.In one embodiment, a portion of the hub bore may be hexagonal shaped, orformed in any other non-circular shape which corresponds to acomplementary shape on the tube to enhance the rotational connectionbetween the hub bore and the tube (not shown). Epoxy or other adhesives(not shown) may also be injected into a space around the stainless steeltube to help prevent the stainless steel tube (not shown) from rotatingrelative to the hub 84. The adhesive also advantageously secures the twocomponents such that the tube (not shown) is less likely to axially pullout of the hub 84.

With continued reference to FIG. 9, the vacuum manifold 86 is preferablyfastened to a vacuum hose 88 at one outlet and to a motor 90 at a secondoutlet. The hub-end of the vacuum manifold 86 desirably houses twosilicone rubber O-rings 85 that function as dynamic (rotatable) sealsbetween the manifold 86 and the steel tube (not shown) which extendsthrough the hub 84. The opposite end of the manifold 86, near theproximal end of the drive tube 24, preferably contains a pair of butylrubber fluid seals 94. These dynamic fluid seals 94 may be lubricatedwith silicone grease. The two fluid seals 94 are mounted back-to-back,with their lips pointing away from each other. In this configuration,the distal seal (i.e., closest to the cutter 22) protects againstpositive pressure leaks such as may be caused by blood pressure and theproximal seal (i.e., closest to the motor 90) excludes air when thesystem is evacuated and the pressure outside the instrument 10 is higherthan the pressure inside the instrument 10.

The vacuum manifold 86 may be connected to the motor 90 through use of athreaded motor face plate 100. The vacuum manifold 86 is preferablythreaded onto the face plate 100 but may be connected in any suitablemanner. The face plate 100 may be attached to the output end of themotor 90 by a threaded fastener 102. The presently preferred motor 90 isa modified 6-volt direct-current hollow-shaft, 22 mm outside diametermotor built by MicroMo.

In the illustrated embodiment, power is transmitted from the motor 90 tothe flexible drive shaft 24 by a length of medium-wall stainless steeltubing that is preferably adhesively-bonded to the drive shaft 24. Thetubing forms a transfer shaft 107 and is preferably coated on the outersurface with approximately 0.001 inch of Type-S Teflon. TheTeflon-coated, exposed ends of the rigid drive shaft, or transfer shaft107, provide a smooth wear-surface for the dynamic fluid seals discussedabove. The transfer shaft tubing may be hypodermic needle stockmeasuring approximately 0.036 inch inside diameter by 0.053 inch outsidediameter, before coating. The transfer shaft 107 desirably is slip fitthrough the approximately 0.058 inch inside diameter of the hollow motorshaft, and desirably extends beyond the length of the motor shaft inboth directions. The slip fit advantageously accommodates axial slidingmovement of the transfer shaft 107 relative to the motor 90 and thebalance of the instrument 10. Thus, axial movability may beaccommodated.

The drive shaft 24 is advantageously capable of axial movement relativeto the motor 90 as described above. Controlled axial movement of thedrive shaft 24, and ultimately the cutter 22 and its connectedcomponents, is desirable regardless of the mechanical connectionallowing such movement. The movement allows the cutter 22 and, in someembodiments, the drive shaft 24 to be withdrawn proximally duringplacement of the catheter sheath, or tubular body 12, in thevasculature. Following positioning, the cutter 22 may then be advancedforward into a cutting position. Such a configuration allows increasedmaneuverability and flexibility during positioning and easier trackingthrough the vasculature. This configuration also allows for easiersterilization of the outer tubular body 12 in a compact coiled package.However, as will be recognized by those of skill in the art, suchrelative axial movement of the cutter 22 and the tubular body 12 is notnecessary for utilization of various other aspects and advantages of thecurrent invention.

A small drive plate 103, bonded to the rear end of the transfer shaft107, advantageously couples with a drive sleeve 105 that is attached tothe approximately 0.078 inch outside diameter motor shaft 92. The driveplate 103 may be any of a number of geometric configurations.Preferably, the drive plate 103 is a rotationally symmetrical shapehaving a central aperture although other configurations may also beused. The symmetry facilitates rotational balancing. In one embodiment,the drive plate 103 is square with a central aperture, triangular with acentral aperture, or circular with a central aperture, with a connectingmember to tie the drive plate to the drive sleeve with a reducedlikelihood of slippage. Together, the drive plate 103 and the drivesleeve 105 form a concentric drive coupling, similar to a splineconnection, between the motor shaft 92 and the transfer shaft 107.

The transfer shaft 107, in turn, may be connected to the flexible driveshaft 24. The concentric drive coupler configuration preferably allowsapproximately 0.25 inch of relative longitudinal movement between thedrive plate 103 and the drive sleeve 105, which is sufficient toaccommodate thermal and mechanical changes in the relative lengths ofthe outer tube 12 and flexible drive tube 24. An integral flange on thedrive plate 103 or the drive sleeve 105 may serve as a shield to deflectfluid away from the rear motor bearings in the event of a leaking fluidseal. Thus, the drive sleeve 105 is preferably a solid walled annularflange which acts as a tubular deflection as will be understood by thoseof skill in the art.

The drive sleeve 105 and the drive plate 103 are preferably molded fromPlexiglas-DR, a medical-grade, toughened acrylic resin made by Rohm andHaas. These parts have shown little tendency to crack in the presence ofthe chemicals that might be present or used in the assembly of thedevice; these chemicals include cyanoacrylate adhesives andaccelerators, motor bearing lubricants, alcohol, epoxies, etc. The drivesleeve 105 and the drive plate 103 are also preferably lightlypress-fitted to their respective shafts 92, 107, and secured with afillet of adhesive applied to the outside of the joints.

With continued reference to FIG. 9, an infusion manifold 108 may bearranged at the proximal end of the control 18. The infusion manifold108 is preferably designed as an input circuit; thus any fluid that canbe pumped or injected at a pressure exceeding the diastolic pressure inthe artery or vein could be used, but saline solutions, therapeuticdrugs and fluoroscope contrast media are most likely to be used withthis device. For instance, saline solutions may be used to purge airfrom the tubular body 12 and drive tube 24 before performing proceduressuch that air embolism may be avoided, and may also be used during anatherectomy procedure to provide a continuous flow of liquid (other thanblood) during cutting to help carry debris through a return circuit. Aswill be recognized, the device 10 generally is purged of air prior toperforming procedures. In such a case, an infusion pump or elevated IVbag may be used to ensure a continuous, low-pressure flow of salinesolution through the system, depending upon the application andprocedure.

At various times during a procedure, the clinician may request that abolus of contrast medium be injected into the instrument 10 to enhance afluoroscopic image of the artery or vein, either to position or todirect the guidewire 28, to locate a blockage, or to confirm that astenosis has indeed been reduced. Contrast medium is a relatively densematerial and high pressure (usually several atmospheres) is usuallyrequired to force the material quickly through the small, elongatedlumen 26 of the drive tube 24. Such a medium may be infused using aninfusion pump, for instance.

In the case of the illustrated surgical instrument 10, the infusionmanifold 108 may be comprised of several components. The first componentmay be an infusion port that may contain a medical infusion valve 109,such as that supplied by Halkey-Roberts Corp. This silicone rubber checkvalve assembly 109 is preferably designed to be opened by insertion of amale Luer-taper (or lock) fitting. The valve 109 more preferably staysopen as long as the taper fitting remains in place, but desirably closesimmediately if it is withdrawn. This action provides simple access whenneeded, but provides the required backflow protection to minimize lossof blood through this route.

The infusion valve 109 is preferably permanently bonded into a side armof a flush port manifold 111, an injection-molded, transparent acrylicfitting. The flush port manifold 111 desirably has an integral threadedextension that may protrude from the proximal side of the control 18.The threaded extension may be provided with a silicone guidewire seal113, and an acetyl (Delrin) guidewire clamp nut 112 that togetherfunction as a hemostasis valve compression-fitting. Delrin may be usedfor the clamp nut 112 to minimize stiction and galling of the threadsduring use. Note that the materials indicated for thecompression-fitting may be varied as will be recognized by those ofskill in the art. An internal shoulder on the threaded portion of thenut 112 advantageously acts as a position stop, preventing extrusion ofthe seal 113 that might otherwise result from over-tightening. Theguidewire 28 desirably extends through both the seal 113 and the nut112.

When the clamp nut 112 is tightened, the guidewire seal 113 may compressagainst the guidewire 28 to lock it in place and to prevent leakage ofblood or air through the seal 113. When it is necessary to slide theguidewire 28, or to slide the surgical instrument 10 along the guidewire28, the clamp nut 112 is first loosened to reduce the clamping actionsomewhat and the relative movement is then initiated. If no guidewire 28is used, the seal 113 may compress against itself and close off thepassageways to reduce or prevent leakage.

A fluid channel advantageously extends through the flush port manifold111, continuing through the open lumen of the drive tube 24, through adistal aperture 39 in the distal extremity of the cutter 22. Theguidewire 28 preferably follows the same path. A leak-proof connectionbetween the flush port manifold 111 and the drive tube 24 is thereforedesirable.

Accordingly, a flush port flange 106 may be bonded to the motor end ofthe flush port manifold 111, creating a chamber housing a low durometerbutyl rubber lip seal 114. The flange 106 may be manufactured of moldedacrylic or the like. The lip seal 114 forms an effective dynamic sealagainst one end of the transfer shaft 107. Lip seals arepressure-compensating devices that function at zero or low pressure bylight elastomeric compression against a shaft, minimizing the dragcomponent in a dynamic application. When pressure against the sealincreases, the lip tightens against the shaft, increasing both thesealing action and the dynamic friction. In this application, however, ahigh pressure sealing requirement preferably is only encountered duringinjection of contrast medium, typically when the cutter 22 is notrotating. Lower pressure dynamic sealing may be required during salineinfusion, however, so pressure compensating lip seals are presentlypreferred.

The lip seal 114 is desirably transfer-molded butyl rubber, with about a0.047 inch inside diameter lip (generally within the range of from about0.035 inch to about 0.050 inch), running on the transfer shaft 107,which may have an outside diameter of approximately 0.055 inch.Medical-grade silicone grease may be used lubricate the interfacebetween the lip seal 114 and the transfer shaft 107, but the greasetends to be forced away from the lip during prolonged use. Thus, aTeflon coating on the transfer shaft 107 may act as a back-up lubricantto reduce or eliminate seal damage in the event the grease is lost.

Returning to the vacuum manifold 86, as illustrated in FIG. 9, thevacuum hose 88 may be attached to the remaining port of the Y-shapedvacuum manifold 86. The hose 88 may be attached in any suitable manneras will be appreciated by those of ordinary skill in the art. The vacuumhose 88 generally extends between the vacuum manifold 86 of the control18 and a vacuum source (see FIG. 1) such as a house vacuum of thecatheter lab of a hospital or a vacuum bottle.

The vacuum hose 88 desirably extends through a switch configuration 120described in detail below. In the illustrated embodiment, the vacuumhose 88 then further extends to the bottom portion of the control 18. Apinch resistant sleeve 116 may be provided to prevent the pinching ofthe vacuum hose 88 as it exits the control 18. Additionally, the pinchresistant sleeve 116 provides a liquid seal to further reduce thelikelihood of liquids entering the control 18 unit during operation.

In interventions such as those with which the present surgicalinstrument 10 has particular utility, it has been discovered to bedesirable that cutting should occur only under sufficient aspiration.Accordingly, an aspect of the present invention involves a cutterlock-out mechanism that will not allow cutting of material unlesssufficient aspiration is present. The aspiration rate may be directlysensed (i.e., flow monitoring) or indirectly sensed (i.e., vacuummonitoring). For instance, because the level of vacuum will typically beone determining factor of the level of aspiration, the vacuum level maybe monitored to determine when a new vacuum bottle should be employed.In such a situation, if the level of a sensed vacuum drops below about15 inches Hg, insufficient clearing vacuum is present and the risk ofblockage within the device 10 increases. Thus, a cutter lock-outmechanism should be employed to prevent cutting of material until thevacuum level is replenished. Specifically, it has been determined that asensed vacuum of about 13.5 to about 14 inches Hg usually precedesclogging in the illustrated embodiment.

The cutter lock-out mechanism is generally comprised of two components,either of which may find utility individually or in combination. One ofthe components is a vacuum monitor. The vacuum monitor (not shown) isdesirably a linear pressure transducer that senses the presence of anadequate vacuum force. The signal from the transducer is preferablyutilized to enable an automatic override of the motor such that themotor cannot turn the cutter 22 if the vacuum drops below a thresholdlevel (e.g. 15 inches Hg). Generally, the vacuum monitor may alsocomprise a vacuum detector, a comparator of any suitable type, an alarmor circuit cut-out. Thus, the vacuum detector may sample the state ofoperation of the vacuum, the comparator may determine varying operatingconditions, and if the vacuum force drops below or unexpectedly andsuddenly exceeds the pre-set threshold level for any reason the alarmcan alert the operator to take corrective action, and/or the cut-outcircuit can automatically stop rotation of the cutter.

The cutter lock-out mechanism may also comprise a flow monitor (notshown). The flow monitor may be of any suitable type and may simplymonitor the flow rate, or aspiration rate, through the aspirationchannel. The flow monitor also may be connected to circuitry or alarmssuch that the user may be warned if the aspiration rate slows (i.e.,conditions indicative of a blockage arise) and/or such that the device10 may automatically take corrective action when a decrease in theaspiration rate is detected. For instance, the device 10 may disablecutting (i.e., rotation of the cutter 22), increase the suction level orotherwise attempt to auto-correct the situation. Also, it is anticipatedthat various alarms, be they visual, tactile or auditory, may beutilized to inform the operator or clinician of the alert status.

Another component of the cutter lock-out mechanism is a switcharrangement that advantageously controls the motor state and vacuumapplication as described below. As will be recognized by those of skillin the art, such a switch may be mechanical, electromechanical, orsoftware-controlled. With reference to FIGS. 9A-9C, a schematicallyillustrated switch configuration 120 desirably assures that the motor 90driving the rotatable drive shaft 24, which in turn drives the cutter22, may not be activated unless the vacuum is being applied. Theillustrated pinch valve switch 120 generally comprises a push buttonoriented along the Z axis shown in FIG. 10A. The switch push button 124may translate along the Z axis when depressed by the user. Desirably,the lower portion of the push button 124 is provided with a u-shaped cutout forming a tunnel along the x-axis. The cut out is preferably sizedto correspond to a compression spring 126 extending therethrough. Thepresently preferred compression spring 126 is a precision-lengthstack-wound button spring fabricated from 0.027″ diameter 302 stainlesssteel wire, with a closed retainer loop at one end. The push button 124may be positioned along a portion of the compression spring 126 suchthat the push button 124 rests on the compression spring 126 and issupported in an up position. The switch push button 124 thus can travelto a down position when depressed by the operator to a position such asthat shown in FIG. 10B. The compression spring 126 provides a bias suchthat the push button 124 will return to the up position when released.Of course, any other suitable biasing mechanism or component may also beused.

The switch push button 124 may be further provided with an axial arm 128that preferably extends in a direction perpendicular to the direction oftravel of the push button 124. Thus, in some embodiments, the arm mayassume an “L” shaped configuration. It is anticipated that a variety ofarm configurations may also be employed.

An electronic switch 130 is desirably located below the axial arm 128 ofthe switch push button 124. Thus, as the push button 124 is furtherdepressed beyond the position in FIG. 10B, to a position such as thatillustrated in FIG. 10C, contact is made on the electrical switch 130.The electrical switch 130, when closed, allows current to flow from apower source 122 to the motor 90. Thus, depression of the push button124 creates a flow of current that drives the motor 90. The motor 90drives the drive tube 24 and cutter 22 of the present surgicalinstrument 10 as described above.

Advantageously, the compression spring 126 is also preferably attachedto a pinching member 132 of the switch configuration 120. As the pushbutton 124 is depressed, the compression spring 126 is advantageouslyinitially deflected. Desirably, the deflection in the compression spring126 causes the pinch member 132 to retract. Thus, the pinch member 132is retracted once the push button 124 is depressed. As the pinch member132 is retracted, a vacuum is initiated and aspiration flow is allowedto pass the pinch valve 120. Advantageously, the amount of flow pastvalve may depend on how far the button 124 is depressed, enablingcontrol of the amount of suction (and, thereby, the level of aspiration)if desired. Further depression of the push button 124 beyond theretraction point initiates a contact of the electrical switch 130 and,therefore, allows the motor 90 to be powered only after the vacuum flowhas begun.

FIG. 10A illustrates a relaxed, non-depressed condition in which thevacuum hose 88 is closed by the pinch valve 132 and the spring 126, andthe electrical switch 130 which controls power supply to the motor 90 isopen. With reference to FIG. 10B, the push button 124 is partiallydepressed, thereby causing the vacuum hose 88 to be opened whilemaintaining the electrical switch 130 open. Further depression of thepush button 124, illustrated in FIG. 10C, closes the electrical switch130 while the vacuum hose 88 is maintained in an open state. Thus,depressing the push button 124 an initial amount starts the vacuum firstand further depression initiates the cutting action. Such timing reducesrisks associated with cutting without aspiration. Because repeatedcycles of opening and closing the valve may tend to shift the positionof the tube 88, internal ribs (not shown) are preferably provided in thecontrol 18 to maintain the proper position of the tube 88.

A return flow path of the illustrated device 10 for aspiration and thelike starts at the cutter 22, passes through the helical thread 46 andthe cutter blocks 42 of the cutter 22 (and stationary blocks of thecutter housing, if present), continues through the outer lumen 20 of theouter tube 12 to the vacuum manifold 86, and then passes through alength of vacuum tubing 88 to a tissue collection/fluid separationcontainer, such as a vacuum bottle. The return flow may be assisted by apositive vacuum supply, such as the vacuum bottle or a house vacuum, asis known in the art. For instance, the collection container may beconnected to a vacuum collection canister that may be, in turn, hookedto a regulated central vacuum source or a suction collection pump orevacuated container.

The pinch valve assembly is preferably designed with a “shippinglock-out” feature (not shown) that secures the button 124 in a partiallydepressed position where the vacuum tube 88 is no longer compressed, butthe switch 130 is not yet actuated. This preserves the elastic memory ofthe pinch tube and protects the device from accidental actuation duringhandling or storage. In its present form, a thin, flexible lock-out wirewith an identifying tag (not shown) can be inserted at the last stage ofinstrument manufacturing, passing through a hole in the button (notshown) and extending through a notch in the side wall of the control 18.In this configuration, a highly-visible tag protrudes from the side ofthe control 18, preventing use of the device until the wire is pulledfree. Removing the lock-out wire releases the button 124 and returns thecontrol 18 to a functional condition. Once removed from the originallocked position, the lock-out wire (not shown) desirably cannot bereinserted without disassembly of the control 18.

With reference again to FIG. 9, the device 10 is preferably controlledby electronic circuitry such as may be contained on a printed circuitboard 133. The circuitry providing the power to the motor 90 may alsoinclude a circuit to check the load on the motor. An exemplary motorcontrol and feedback circuit is illustrated in FIG. 11; however, as willbe readily recognized by those of ordinary skill in the art, many othermotor control circuits may also be implemented. As is known, when adirect current motor, as used in this invention, encounters resistanceto rotational movement, an increased load is placed on the power source122. Accordingly, as described below, the circuitry is provided with thecapability to identify, indicate, record and possibly compare the speedand/or torque to previously recorded speeds or torques. Specifically,the speed and/or torque, as indicated by the level of current to themotor, may be compared over time through the use of a comparator.Additionally, a reverse switch may be provided to reverse out of jams orpotential jams when necessary. Such a reverse switch may be a momentaryswitch or any other suitable switch as will be recognized by those ofskill in the art.

As described below in detail, a motor controller 134 preferably providesthe motor 90 with sufficient energy by using a combination of missingpulse and pulse width modulation. For instance, the motor speed may besensed by measuring the back electromotive force (EMF), which isproportional to speed. A portion of the back EMF may be fed to thecontroller 134, which preferably varies the drive power to the motor 90to maintain a constant speed. The circuit values of the controller 134allow motor speed settings of about 1,000 RPM to about 8,000 RPM. Thespeed chosen for no load operation in one embodiment may preferablyrange from approximately 1,500 RPM to about 5,000 RPM. In a presentlypreferred embodiment, the no load operation speed is approximately 2,000RPM. Desirably, the motor speeds associated with the present inventionare less than those associated with abrasive-type devices andturbulence-based devices as will be recognized by those of skill in theart. In some embodiments, the motor control circuitry may limit themotor torque to a range of about 0.10 oz-inches to about 0.45 oz-inchesby sensing the motor current and setting the motor drive power to theappropriate level. A switching controller, thus, may be used for tworeasons: (a) it is very efficient—it uses less than 0.015 amperes (themotor current would vary from 0.05 to 0.4 amperes, or perhaps more), and(b) it can deliver appropriate torque instantly or on demand, even atlow motor speeds, so the likelihood of stalling is minimized.

The power source 122, preferably a 9-volt battery, may not beelectrically connected to the controller 134 until the push button 124is depressed, as discussed above, so standby power drain isadvantageously eliminated or reduced. In the illustrated embodiment, alight emitting diode (LED) is desirably on when the motor is running atnormal loads (i.e., the sensed current level is lower than apredetermined current level requiring an alert). This LED may be greenin some embodiments and will be referred to as such in connection withthe illustrated embodiment. Another LED turns on at a motor current ofapproximately 0.25 amperes, or another threshold level that may indicatea motor “overload” situation. This LED may be red in some embodimentsand will be referred to as such in connection with the illustratedembodiment. For instance, the red LED may indicate that the current isproximate, or has achieved, a predetermined maximum safe value. Thepreset maximum safe value is the upper limit, as determined by thespecific design and configuration of the device 10, for current thatindicates an overload condition. Thus, another feature of the presentinvention includes the ability to provide feedback to the operator basedupon motor load. This is advantageous in that the operator can bealerted to a potential binding of the instrument and react accordingly.For instance, the progression rate of the instrument may be reduced orstopped or the instrument may be backed from the trouble location usingthe reverse switch or otherwise. It should also be understood that thedevice may make automatic adjustments to the motor speed relative to thesensed load utilizing methods which would be readily apparent to oneskilled in the art following a review of FIG. 11.

Any of a variety of tactile, auditory or visual alarms may also beprovided either in combination with, or as alternatives to, each otherand the LEDs. For instance, the surgical instrument could vibrate orprovide an audible signal when it encounters an overload situation. Thepulses or tones may vary to correspond to any variance in resistance torotation. For example, the pitch may increase with resistance or thespeed of a repeating pulse of sound may increase. Additionally, where a(CRT) monitor is used to visualize the operation, a visual signal couldbe sent to the monitor to display the operating characteristics of thesurgical equipment. As will be further recognized to those skilled inthe art, other variations of alerting the operator to the operatingcharacteristics of the present invention may be provided.

The present invention thus provides feedback to the clinician in realtime during the progress of the rotational atherectomy procedure. Realtime feedback can allow the clinician to adjust the procedure inresponse to circumstances that may vary from procedure to procedure,thereby enhancing the overall efficiency of the procedure and possiblyminimizing additional risks such as the creation of emboli. Pressing thecutter 22 into a lesion with too much force may produce an increasedload, which can then be detected by the circuitry 131 and communicatedto the clinician in any of a variety of ways as has been discussed. Thismay allow the clinician to ease back on the distal advancement forceand/or adjust the vacuum or RPM of the cutter 22, such as by reducingthe advancement force and lowering the resistance to rotation of thecutter 22, until the load is reduced to an acceptable level, andcontinue with the procedure. As will be recognized, if aspiration dropsdue to increased material being aspirated, the load is likely to haveincreased; therefore, the clinician is alerted to such an increase inload such that corrective action may be taken. By allowing the load toreturn to an acceptable level, the aspiration rate may also return to anacceptable level in some embodiments. As will be recognized, the loadmay increase due to a blockage and the blockage would lower theaspiration rate; however, clearing the blockage will generally returnthe aspiration rate to a desired level as well as reduce the load on themotor.

In addition, increased load can be incurred by kinks at any locationalong the length of the instrument, thereby reducing the motor speed.Kink-originated loading could be reflected in the feedback mechanism tothe clinician, so that the clinician can assess what corrective actionto take.

Another aspect of the present invention involves a selectivelyreversible tip rotation. For instance, the drive motor may be reversedsuch as by manipulation of the reverse control switch (not shown) on thehandle of the control 18. Motor reversing circuitry, with or without avariable speed control, is well understood by those of skill in the art.Momentary reversing of the direction of rotation of the distal cutter,most likely at a relatively low speed of rotation, may be desirable todislodge material which may have become jammed in the cutter tip. Inthis manner, the clinician may be able to clear a cutter tip blockagewithout needing to remove the catheter from the patient and incur theadditional time and effort of clearing the tip and replacing the device.Low speed reverse rotation of the cutter may be accomplished incombination with a relatively increased vacuum, to reduce the likelihoodof dislodging emboli into the blood stream. Following a brief period ofreverse rotation, forward rotation of the cutter tip can be resumed.Whether the obstruction has been successfully dislodged from the cuttertip will be apparent to the clinician through the feedback mechanismsdiscussed above. Moreover, it is anticipated that the device mayalternatively have substantially the same torque, speed, vacuum force,and alarm thresholds when the cutter is rotated in either direction. Itis, however, presently preferred to utilize the same speed of rotationin both forward and reverse rotation.

In the presently preferred embodiment of the control and power supplycircuitry illustrated in FIG. 11, the motor controller has an LM3578Aswitching regulator, indicated generally by U1 in FIG. 11. The switchingregulator may be an LM3578A switching regulator in some embodiments; oneof ordinary skill in the art will readily recognize other components andcircuitry that can perform essentially the same functions. The switchingregulator is normally used as a power supply regulator, wherein it mayprovide a substantially constant voltage regardless of load. A negativein jack (pin 1) may be used as an error input. For instance, when thevoltage at pin 1 is less than about 1 volt, an inference may beestablished that the motor speed may be too low, therefore the outputjack (pin 6) goes low. When the output at pin 6 goes low, it may cause agate (pin G) of Q1 to be near 0 volts. As will be recognized, this maycause Q1 to turn on with a resistance of about 1.3 ohms in theillustrated embodiment. Advantageously, the end result is that themotor, Q1, D1 and R4 may be connected in series across the battery. Themotor current will likely be rather heavy, so the motor speed mayincrease. This “on” condition lasts for a time that is preferablycontrolled by U1's oscillator, whose frequency (about 500 Hz) may be setby C4. Also, the switching regulator U1 desirably limits the output ontime to about 90% of this 2-millisecond period (1/frequency=period)because it uses the first 10% portion purely for comparing the errorsignal to the reference. The comparison advantageously continues duringthe 90% period, with the output on or off as determined by the errorsignal. If the motor speed were to increase to the proper level duringthe 90% portion of the cycle, the output would preferably shut offimmediately, thereby resulting in a narrowed pulse. Hence, pulse widthmodulation is achieved.

Desirably, the output of the switching regulator U1 only goes low, so R1preferably pulls the output high when the switching regulator U1 is off.R13 isolates the switching regulator U1 from the gate capacitance of Q1,thereby advantageously ensuring a more reliable start-up of theswitching regulator U1 upon application of power. D1 preferably preventsbelow-ground motor switching transients from reaching the transistor Q1.In the illustrated embodiment, the VP2204 may have a 40-volt rating,which advantageously provides plenty of margin for withstanding voltagetransients. As will be recognized by those of skill in the art, anyother suitable control circuit may also be utilized. Power supply filterC5 preferably helps provide the large short duration currents demandedby the controller, especially when the battery power is nearly depleted.

In the illustrated embodiment, an N-channel FET, indicated by referencenumerals Q2, preferably switches the motor's back EMF to a storagecapacitor C2 during the portion of the control cycle when the motor isnot powered (i.e., Q2 is off when Q1 is on, and vice versa). Theresistor R2, along with the gate capacitance of the FET Q2,advantageously forms a delay network so that when the FET Q2 turns onafter the FET Q1 turns off. This configuration may block turn-offtransients and may present a voltage to C2 that more accurately reflectsthe back EMF. The FET's Q2 turn-off need not be delayed, so D2 may turnon with negative-going signals and may parallel the resistor R2 with alow impedance, thereby giving only a slight delay. A resistor R5 and aresistor R6 preferably divide the back EMF to provide the error voltage(nominally about 1 volt) to pin 1 of the switching regulator U1. Thevalue of the resistor R5 desirably determines the level of back EMF,and, therefore, the motor speed required to produce about 1 volt at theswitching regulator U1, pin 1.

The resistor R4 may be in series with the motor and may be used to sensethe motor current and limit the motor torque accordingly. For instance,the current pulses through the resistor R4 generate voltage pulses,which may be integrated (averaged) by the resistor R3 and the capacitorC1 and fed to pin 7 of the switching regulator U1, which is the currentlimit input. Preferably, when the voltage at this pin is about 0.110volts or more, the switching regulator U1 may not increase the outputdrive, regardless of the error voltage. The circuit values shown resultin about 0.45 amp average, or between about 0.45 and about 0.5 oz-in. ofstall torque for the motor.

The back EMF voltage stored by the capacitor C2 is preferably furtherfiltered by a resistor R7 and a capacitor C3 and may appear at theoutput (pin 7) of an amplifier (U2) as a relatively noise-free signalwhich follows the motor speed with a slight time lag. The amplifier inthe illustrated embodiment is an LM358 buffer amplifier. The voltage isdesirably divided by a resistor R8, a resistor R9 and a resistor R10 andmay appear at the positive input of the comparator section of theamplifier U2 (pin 3). A negative input is desirably fixed at about 1volt, since it is connected to the switching regulator U1, pin 2. Whenthe voltage at pin 3 exceeds that at pin 2, the output (pin 1) is highand the green (Cutting) LED is on in the illustrated embodiment. Whenthe voltage at pin 3 is less than at pin 2, the output is low and thered (Overload) LED is on in the illustrated embodiment. “Overload” inthe embodiment being described herein has been defined as the point whenthe motor current reaches about 70% of stall current; however, anydesired percentage of stall current may be used to define an overloadcondition. The value of a resistor R9 determines approximately equal redand green LED intensities with a dynamic motor load that causes a motorcurrent of approximately 0.35 amperes.

With continued reference to FIG. 11, a test connector P2 providessignals and voltages for production testing of the controller board,which may be tested as a subassembly prior to installation. The testconnector P2 may also be accessible when the top half of the housing isremoved, such as for testing at higher levels of assembly. It should beappreciated that one of skill in the art may modify the test connectorand related circuitry such that the connector could also become a databus all data to be passed from the control to a recorder, a display orthe like.

In a presently preferred method of use, a guidewire 28 is firstpercutaneously introduced and transluminally advanced in accordance withwell known techniques to the obstruction to be cleared. The surgicalinstrument 10 is then introduced by placing the distal end 16 of theflexible tubular body 12 on the guidewire 28, and advancing the flexibletubular body 12 along the guidewire 28 through the vessel to thetreatment site. When the distal end 16 of the flexible tubular body 12has been maneuvered into the correct position adjacent the proximalterminus of material to be removed, the drive tube 24 is rotatedrelative to the tubular body 12 to cause the cutter 22 to rotate in adirection which will cause the forward end 47 of the thread 46 to drawmaterial into the housing 21. A circular cutting action may be providedby mutual cooperation of the outer cutting edge of the screw thread 46with lip 39 of the cutter housing 21 and the internal peripheral wall ofthe cutter housing 21. In addition, the cutter housing 21 in cooperationwith the flanges 42 and any other stationary members present,effectively chops or minces the strands of material being drawn into thecutter housing 21. The cut material is then carried proximally throughthe annular passageway between the flexible drive tube 24 and thetubular body 12 under the force of vacuum. If an increase in load and/ordecrease in RPM is detected, the clinician can take reactive measures asdescribed above. The vacuum preferably pulls the cuttings through theentire length of the lumen 20 and vacuum tube 88 and into a suitabledisposal receptacle. A manual or automatic regulator may regulate thevacuum source such that a constant flow velocity may be maintained, orblockages reduced or cleared, through the vacuum tube 88 regardless ofthe viscosity of the material passing through the vacuum tube 88.

With reference now to FIG. 12, a further aspect of the presentrotational atherectomy device will be described in detail. Asillustrated, the elongate flexible member 12 preferably includes anexpandable component 150 near the distal end 16 of the flexible member12. More preferably, the expandable component 150 is positionedproximate the cutter housing 21 at a location directly adjacent theproximate end of the housing 21. In some embodiments, the expandablemember 150 may be positioned on the housing 21 itself.

The expandable member 150 preferably extends about only a portion of thetotal circumference of the flexible member 12. In this regard, theexpandable member is used to offset the cutter tip 22 such that the axisof rotation of the cutter tip is disposed about a second axis that isgenerally parallel to an axis of the artery in which the device isdisposed but the cutter tip axis is laterally displaced from the axis ofthe artery. Specifically, as the expandable member 150 is inflated, orexpanded, the expandable member 150 contacts one of the sides of theartery, thereby displacing the flexible member 12 and the cutter tip 22in a radial direction away from the center of the artery. In theillustrated embodiment, the expandable member 150 extends about 75°around the circumference of the flexible member 12. In otherembodiments, the expandable member may extend around between about 45°to about 270°.

The expandable member may comprise any of a number of components. Forinstance, the illustrated expandable member is a Pellethane balloonhaving eccentric tails 152. The presently preferred material,Pellethane, forms a compliant balloon that allows the diameter to growwith increases in inflation pressure. The preferred variant ofPellethane is 2363-90AE which allows a working pressure of between about10 psi and about 60 psi with diameter growths of between about 1.5 mm toabout 2.0 mm. Of course, other materials may be chosen depending uponthe application. In other embodiments, the working pressure may rangefrom about 5 psi and about 50 psi with diameter growths of between about0.8 mm and about 3.0 mm. The inflatable portion of the balloonpreferably has an axial length of between about 8 mm and 2 mm with amore preferred length being about 5 mm. In arrangements having aninflatable length of about 5 mm, it is anticipated that about 3 mm ofthe balloon will be useful in offsetting the cutter tip 22 relative toan axis of the lumen in which the cutter tip 22 is disposed.

The eccentric tails 152 of the balloon also form a part of the presentlypreferred arrangement. The eccentric tails 152 generally lie flat alongthe flexible member 12 to which they are attached. Such an arrangementallows the deflated profile of the device 10 to be decreased as well aseases the bonding between the expandable member 150 and the flexiblemember 12. While concentric tailed balloons may adequately function asthe expandable member 150, the eccentric tailed balloons are presentlypreferred. The tails are preferably adhered to the flexible member withan epoxy resin or ultraviolet adhesive. In some arrangements, the tails152 are preferably captured by external rings, housings or tubes.

An inflation lumen 154 extends between the expandable member 150 and aportion of the device 10 which is external to a patient. The lumen 154may be formed within the flexible member 12 or may be positioned to theoutside of the flexible member 12. The positioning of the inflationlumen 154 may be selected as a result of the application in which thedevice 10 will be used.

In use, the device 10 featuring the balloon operates in a similar mannerto the device 10 described above. Specifically, as described above, theguidewire 28 is first percutaneously introduced and transluminallyadvanced in accordance with well known techniques to the obstruction tobe cleared. The surgical instrument 10 is then introduced by placing thedistal end 16 of the flexible tubular body 12 on the guidewire 28, andadvancing the flexible tubular body 12 along the guidewire 28 throughthe vessel to the treatment site. When the distal end 16 of the flexibletubular body 12 has been maneuvered into the correct position adjacentthe proximal terminus of material to be removed, the expandable elementis inflated with a fluid in a known manner. The expandable member 150acts as a deflecting mechanism to offset the cutter tip 22 from thecenterline of the artery.

At this point, any of at least two modes of operation may be used. In afirst mode, illustrated schematically in FIG. 13, the drive tube 24 isrotated relative to the tubular body 12 to cause the cutter 22 to rotatein a direction which will cause the forward end 47 of the thread 46 todraw material into the housing 21. Also, suction may be used to pullmaterial into the housing 21. A circular cutting action may be providedby mutual cooperation of the outer cutting edge of the screw thread 46with lip 39 of the cutter housing 21 and the internal peripheral wall ofthe cutter housing 21. In addition, the cutter housing 21 in cooperationwith the flanges 42 and any other stationary members present,effectively chops or minces the strands of material being drawn into thecutter housing 21.

The cutter tip 22 is then rotated in an eccentric rotation by turningthe flexible member 12 while the cutter tip 22 is spinning in thehousing 22. In one arrangement, the cutter tip is eccentrically rotatedthrough a pass of about 360°; however, the sweep of the cutter tip maybe varied depending upon any one of a number of factors. Also, therotation of the flexible member 12 may be performed manually. After acomplete rotation of the flexible member 12, the cutter tip 12 is thenadvanced forward through another portion of the material to be removed.The cut material is carried proximally through the annular passagewaybetween the flexible drive tube 24 and the tubular body 12 under theforce of vacuum. If an increase in load and/or decrease in RPM isdetected, the clinician can take reactive measures as described above.The vacuum preferably pulls the cuttings through the entire length ofthe lumen 20 and vacuum tube 88 and into a suitable disposal receptacle.A manual or automatic regulator may regulate the vacuum source such thata constant flow velocity may be maintained, or blockages reduced orcleared, through the vacuum tube 88 regardless of the viscosity of thematerial passing through the vacuum tube 88.

In another mode of operation, illustrated schematically in FIG. 14, thecutter tip 22 is axially advanced through the material to be removedafter the deflecting expandable member 150 is inflated. A circularcutting action may be provided by mutual cooperation of the outercutting edge of the screw thread 46 with lip 39 of the cutter housing 21and the internal peripheral wall of the cutter housing 21. In addition,the cutter housing 21 in cooperation with the flanges 42 and any otherstationary members present, effectively chops or minces the strands ofmaterial being drawn into the cutter housing 21. The cut material iscarried proximally through the annular passageway between the flexibledrive tube 24 and the tubular body 12 under the force of vacuum. If anincrease in load and/or decrease in RPM is detected, the clinician cantake reactive measures as described above. The vacuum preferably pullsthe cuttings through the entire length of the lumen 20 and vacuum tube88 and into a suitable disposal receptacle. A manual or automaticregulator may regulate the vacuum source such that a constant flowvelocity may be maintained, or blockages reduced or cleared, through thevacuum tube 88 regardless of the viscosity of the material passingthrough the vacuum tube 88.

After the cutter tip 22 has traversed the length of the material to beremoved, the cutter tip 22 is withdrawn through substantially the samepath of axial travel through the material. The expandable member 150 isthen deflated and the flexible member 12 is reoriented for a second passthrough the material. In some arrangements, the expandable member 150may remain inflated or may be partially deflated during reorientation.The flexible member 12 may be rotated to any degree desired by theoperator. In one arrangement, the flexible member 12 is rotated about 60degrees from the first pass. This arrangement is illustratedschematically in FIG. 14. The expandable member 150 is then inflated andthe cutter tip 22 is again axially advanced through the material to beremoved. This process is repeated as desired in any particularapplication. In the illustrated arrangement, a non-offset pass is alsoperformed such that the cutter tip 22 passes through a generally centrallocation. One of ordinary skill in the art will readily recognize thatthe degree of overlap between passes may vary from operator to operator.Also, in instances in which the overlap is not extensive, the pathsformed by the individual passes may coalesce into a single lumen.

As will be recognized, either of the above described modes of operationwill result in an enlarged effective flow path as compared to theoutside diameter of the device. It should be recognized that anycombination of the modes of use of the deflection expandable memberdiscussed directly above may also be used. The off-center cuttingarrangement advantageously implements the device 10 in an operationwhich enlarges the diameter of the cleared material over and above theoutside diameter of the catheter being used to house the cutter.

Although this invention has been described in terms of certain preferredembodiments, other embodiments apparent to those of ordinary skill inthe art are also within the scope of this invention. Accordingly, thescope of this invention is intended to be defined only by the claimsthat follow.

1. A method of removing thrombus material from a thrombectomy site, themethod comprising: providing a rotational medical device comprising: anelongate flexible tubular body having a proximal end, a distal end, andan elongate central lumen; a rotational operating tip disposed at thedistal end of the tubular body and operably connected to a motor; and avacuum system coupled to said elongate flexible tubular body, saidvacuum system comprising: a vacuum manifold having a first outlet and asecond outlet, said vacuum manifold being connected to a vacuum sourceat said first outlet and the motor at said second outlet; a vacuumsensor; and a lock-out mechanism configured to control the motor basedon a sensed vacuum level, the lock-out mechanism configured to preventrotation of the operating tip when the sensed vacuum level is below apredetermined threshold; placing said distal end of said elongateflexible tubular body in proximity to a thrombus at said thrombectomysite; and activating said vacuum system such that a portion of saidthrombus is drawn into said elongate central lumen.
 2. The method ofremoving thrombus material of claim 1, further comprising powering saidmotor.
 3. The method of removing thrombus material of claim 1, whereinthe providing step further comprises providing the rotational operatingtip with a cutter.
 4. The method of removing thrombus material of claim1, wherein the sensed vacuum level is sufficient for operable aspirationof said thrombus at said thrombectomy site.
 5. The method of removingthrombus material of claim 1, wherein the providing step furthercomprises the lock-out mechanism to be configured to automaticallycoordinate operation of the motor and operating tip based on the sensedvacuum level.
 6. The method of removing thrombus material of claim 5,wherein the operation of the motor coincides with a sensed vacuum levelof 15 in Hg or more.
 7. The method of removing thrombus material ofclaim 1, wherein the providing step further comprises the lock-outmechanism with a push button, the push button having a depressedconfiguration configured to drive the motor after connecting theelongate tubular body with the vacuum source.
 8. The method of removingthrombus material of claim 7, the depressed configuration configured todrive the motor with a preset time delay after connecting the elongatetubular body with the vacuum source.